CRANIAL NERVE EXAM: NORMAL EXAM
Cranial Nerve 1 - Olfaction
This CN is tested one nostril at a time by using a nonirritating smell such as tobacco, orange, vanilla, coffee, etc. Detection of the smell is more important than the actual identification.
Cranial Nerve 2 - Visual acuity
The first step in assessing the optic nerve is testing visual acuity. This can be done with a standard Snellen chart or with a pocket chart (Rosenbaum). Have the patient use their glasses if needed to obtain best-corrected vision. Have the patient hold the pocket chart at the focal length that is best for them which is usually 14 inches. Have them recite the line with the smallest letters that they can read and record the acuity.
Cranial Nerve 2 - Visual fields
There are several different screening tests that can be used to assess visual fields at the bedside. First hold up both hands superiorly and inferiorly and ask the patient if they can see both hands and do they look symmetric. Then test each eye individually using your fingers in the four quadrants of the visual field and ask the patient to count fingers held up or point to the hand when a finger wiggles using yourself as a control. A second screening test is to use a grid card. Have the patient focus on the dot in the center of the grid then ask if any part of the grid is missing or looks different. A third method is to use a cotton tip applicator. Testing one eye at a time ask the patient to say "now" as soon as they see the applicator come into their side vision as they focus on the examiner's nose. All of these tests are screening tests. Formal perimetry is the most accurate way of assessing visual fields.
Cranial Nerve 2 - Fundoscopy
Direct visualization of the optic nerve head is an important and valuable part of assessing CN 2. Systematically look at the optic disc, vessels, retinal background and fovea.
Cranial Nerves 2 & 3 - Pupillary Light Reflex
The afferent or sensory limb of the pupillary light reflex is CN2 while the efferent or motor limb is the parasympathetics of CN3. Shine a flashlight into each eye noting the direct as well as the consensual constriction of the pupils.
The swinging flashlight test is used to test for a relative afferent pupillary defect or a Marcus Gunn pupil. Swinging the flashlight back and forth between the two eyes identifies if one pupil has less light perception than the other. Shine the flashlight at one eye noting the size of both pupils. Then swing the flashlight to the other eye. If both pupils now dilate then that eye has perceived less light stimulus (a defect in the sensory or afferent pathway) than the opposite eye.
Cranial Nerves 3, 4 & 6 - Inspection and Ocular Alignment
Before checking ocular movements it is important to inspect the eyes. Look for ptosis. Note the appearance of the eyes and check for ocular alignment (the reflection of your light source should fall on the same location of each eyeball).
Cranial Nerves 3, 4 & 6 - Versions
Testing extraocular range of motion with both eyes open and following the target (conjugate gaze) is called versions. The patient is asked to follow a target through the six principle positions of gaze. Note any misalignment of the eyes or complaint of diplopia (double vision).
Cranial Nerves 3, 4 & 6 - Ductions
If there is any misalignment of the eyes or diplopia on versions it is important to then examine each eye with the other covered (this is called ductions). The patient should follow an object through the six principle positions of gaze so each extraocular muscle's function is tested.
Supranuclear gaze systems - Introduction
The purpose of supranuclear control of gaze is to insure that the image that is being looked at is centered or maintained on the fovea of the retina. The following maneuvers test the major systems that control eye movements.
Saccades are tested by holding up your two hands about three feet apart and instructing the patient to look at the finger that is wiggling without moving their head. The patient's eyes should be able to quickly, smoothly and accurately jump from target to target.
To test Smooth Pursuit ask the patient to keep watching the target without moving their head. Then move the target slowly from side to side and up and down. The eyes should be able to follow the target smoothly without lagging behind or jerking to catch up with the target.
Optokinetic Nystagmus is a test of smooth pursuit with quick resetting saccades. Use a tape with repeating shapes on it and ask the patient to look at each new object as it appears as you run the tape between your fingers to the right, left, up, and down. The patient will have brief pursuit eye movements in the direction of the tape movement with quick saccades or jerks in the opposite direction. The resetting saccades are easier to observe than the brief pursuit movement.
The vestibulo-ocular reflex is obtained by having the patient visually fixate on an object straight ahead, then rapidly turning the patient's head form side to side and up and down. The eyes should stay fixed on the object and turn in the opposite direction of the head movement.
Vergence eye movements occur when the eyes move simultaneously inward (convergence) or outward (divergence) in order to maintain the image on the fovea that is close up or far away. Most often convergence is tested as part of the near triad. When a patient is asked to follow an object that is brought from a distance to the tip of their nose the eyes should converge, the pupil will constrict and the lens will round up (accommodation).
Cranial Nerve 5 - Sensory
Test for both light touch (cotton tip applicator) and pain (sharp object) in the 3 sensory divisions (forehead, cheek, and jaw) of CN 5.
Cranial Nerves 5 & 7 - Corneal reflex
The ophthalmic division (V1) of the 5th nerve is the sensory or afferent limb and a branch of the 7th nerve to the orbicularis oculi muscle is the motor or efferent limb of the corneal reflex. The limbal junction of the cornea is lightly touched with a strand of cotton. The patient is asked if they feel the touch as well as the examiner observing the reflex blink.
Cranial Nerve 5 - Motor
The motor division of CN 5 supplies the muscles of mastication (temporalis, masseters, and pterygoids). Palpate the temporalis and masseter muscles as the patient bites down hard. Then have the patient open their mouth and resist the examiner's attempt to close the mouth. If there is weakness of the pterygoids the jaw will deviate towards the side of the weakness. The last test for this nerve is testing for a jaw jerk, which is a stretch reflex. Have the patient slightly open their mouth then place your finger on their chin and strike your finger with a reflex hammer. Normally there is no movement. If there is a jaw jerk it is said to be positive and this indicates an upper motor neuron lesion.
Cranial Nerve 7 - Motor
The motor division of CN 7 supplies the muscles of facial expression. Start from the top and work down. Have the patient wrinkle forehead (frontalis muscle), close eyes tight (orbicularis oculi) show their teeth (buccinator), and purse lips or blow a kiss (orbicularis oris). If there is weakness especially in a bilateral upper motor neuron distribution, get the patient to smile by telling a joke or funny story. With a pseudobulbar palsy automatic or emotional facial expression will be more complete than movements to command.
Cranial Nerve 7 - Sensory, Taste
Taste is the sensory modality tested for the sensory division of CN 7. The examiner can use a cotton tip applicator dipped in a solution that is sweet, salty, sour, or bitter. Apply to one side then the other side of the extended tongue and have the patient decide on the taste before they pull their tongue back in to tell you their answer.
Cranial Nerve 8 - Auditory Acuity, Weber & Rinne Tests
The cochlear division of CN 8 is tested by screening for auditory acuity. This can be done by the examiner lightly rubbing their fingers by each ear or by using a ticking watch. Compare right versus left. Further screening for conduction versus neurosensory hearing loss can be accomplished by using the Weber and Rinne tests. The Weber test consists of placing a vibrating tuning fork on the middle of the head and asking if the patient feels or hears it best on one side or the other. The normal patient will say it is the same in both ears. The patient with unilateral neurosensory hearing loss will hear it best in the normal ear while the patient with a unilateral conductive hearing loss will hear it best in the abnormal ear. The Rinne test consists of comparing bone conduction (placing the tuning fork on the mastoid process) versus air conduction (placing the tuning fork in front of the pinna). Normally, air conduction is greater than bone conduction. For neurosensory hearing loss air conduction is still greater than bone conduction but for conduction hearing loss bone conduction will be greater than air conduction.
Cranial Nerve 8 - Vestibular
The vestibular division of CN 8 can be tested for by using the vestibulo-ocular reflex as already demonstrated or by using ice water calorics to test vestibular function. The later test is usually reserved for patients who have vertigo or balance problems or in the comatose patient when one is testing brainstem function.
Cranial Nerves 9 & 10 - Motor
The motor division of CN 9 & 10 is tested by having the patient say "ah" or "kah". The palate should rise symmetrically and there should be little nasal air escape. With unilateral weakness the uvula will deviate toward the normal side because that side of the palate is pulled up higher. With bilateral weakness neither side of the palate will elevate and there will be marked nasal air escape.
Cranial Nerves 9 & 10 - Sensory and Motor: Gag Reflex
The gag reflex tests both the sensory and motor components of CN 9 & 10. This involuntary reflex is obtained by touching the back of the pharynx with the tongue depressor and watching the elevation of the palate.
Cranial Nerve 11 - Motor
CN 11 is tested by asking the patient to shrug their shoulders (trapezius muscles) and turn their head (sternocleidomastoid muscles) against resistance.
Cranial Nerve 12 - Motor
The 12th CN is tested by having the patient stick out their tongue and move it side to side. Further strength testing can be done by having the patient push the tongue against a tongue blade. Inspect the tongue for atrophy and fasciculations. If there is unilateral weakness, the protruded tongue will deviate towards the weak side.
By having the patient say lah-pah-kah, the examiner is testing the motor components of CN 12, 7, and 9&10.